This invention relates to novel spiro-thienohydantoin derivatives useful in the treatment of certain chronic complications arising from diabetes mellitus, such as diabetic cataracts and neuropathy, to pharmaceutical compositions containing such compounds and to a method of using these compounds. In the past various attempts have been made to obtain new and more effective oral antidiabetic agents. Generally, these efforts have involved synthesis of new organic compounds, particularly sulfonyl ureas, and determination of their ability to substantially lower blood sugar levels when administered orally. However, little is known about the effect of organic compounds in preventing or alleviating chronic complications of diabetes, such as diabetic cataracts, neuropathy and retinopathy. U.S. Pat. No. 3,821,383 discloses aldose reductase inhibitors like 1,3-dioxo-1H-benz[d, e]-isoquinoline-2(3H)-acetic acid and derivatives thereof to be useful for the treatment of these conditions, even though these particular compounds are not known to be hypoglycemic in nature. Such aldose reductase inhibitors function by inhibiting the activity of the enzyme aldose reductase, which is primarily responsible for regulating the reduction of aldoses, such as glucose and galactose, to the corresponding polyols, such as sorbitol and galactitol, in humans and other animals. In this way, unwanted accumulations of galactitol in the lens of galactosemic subjects and of sorbitol in the lens, peripheral nervous cord and kidney of various diabetic subjects are prevented or reduced. Accordingly, such compounds are of theraupeutic value as aldose reductase inhibitors for controlling certain chronic diabetic complications, including those of an ocular nature, since it is known in the art that the presence of polyols in the lens of the eye leads to cataract formation, with a concomitant loss of lens clarity.